The present invention is an improvement over the sheet feeding apparatus disclosed in U.S. Pat. No. 4,437,657, granted Mar. 20, 1984. As disclosed therein, the feeding apparatus includes a fairly large number (e.g. 10) of fixed-in-position spaced suction cups supported on a common support or mounting member which may be a rigid pneumatic feed tube. The suction cup support member is movable between an initially lowered position and a raised position where the suction planes of the suction cups are parallel to and engage the bottom exposed surface of the bottommost sheet in a stack of the same held in a top loadable stacking frame, so that the operation of the apparatus does not have to be interrupted when the supply of sheets is to be replenished. The stack of sheets preferably rests on a slightly forwardly inclined support tray which terminates short of the lower front end of the stack to leave an opening running the entire width of the stack to expose thereat the bottom sheet in the stack for engagement by one or more of the suction cups. The front end of the stack rests on longitudinally adjustable flexible support lips so that when the bottommost sheet is pulled from the stack by the lowering of the suction cups, the sheet deflects and wipes by the deflected lips, which spring back to retain the next sheet within the stacking frame.
As disclosed in this patent, the suction cups described are pivotally supported with respect to the means which raises and lowers them so that the suction cups have uniquely tilted positions with respect to the bottommost sheet in the stack of sheets involved, which ensures that only the bottommost sheet is withdrawn from the stack for sheets of widely varying flexibility. To avoid the necessity of moving the suction cups bodily horizontally away from the rigid support ledge previously needed to clear the same, which sometimes had caused slippage and premature release of the suction cups from rigid sheet materials, the suction cups are moved only relatively slightly, if at all, in a horizontal direction away from the flexible lip support ledges described. This permits the removal of the bottommost sheet by a primarily downward movement thereof, where the front end of even a relatively rigid sheet of material can be pulled easily by the flexible support ledge-forming lips by a wiping, lip-flexing action, as previously described.
Flanged brackets rigidly extend from the ends of the suction cup support member, the brackets having vertical portions pivotally supported and carried upon the ends of a pair of remotely pivoted crank arms which are raised and lowered to move the suction cups carried by the support member between the lowered and raised positions described. Spring means extend between the crank arms and horizontal flanges on the brackets at the ends of the suction cup support member to urge the latter into a stable position, where the suction planes of the suction cups are parallel to each other.
When the suction cups are raised to an elevation slightly below a point where they contact the bottommost sheet in the stack, the bracket flanges initially engage one or more vertically adjustable abutment shoulders at a point spaced from the pivot axis, so that a small additional upward movement of the suction cup support member results in pivoting of the member on the link arms. In this position of the suction cup support member, the suction planes of the suction cups are almost parallel to this sheet, so that when the support member is raised further to effect this contact, the suction planes are substantially parallel thereto. The support member is raised slightly above this position of initial suction cup contact where it and the suction cups carried thereon are pivoted substantially rapidly in a direction to tilt the suction cup planes away from the flexible support ledge, without significantly shifting the horizontal position of the suction cups along the sheet. The latter pivoting action separates the bottommost sheet from the other sheets in the stack without causing separation of the suction cups from the bottommost sheet.
The crank arms and suction cup support member are then lowered to bring the front end of the sheet partially pulled from the stack thereof against the top and front portion of a drive roller. As the suction cups are thus lowered, idler pressure rollers carried on the ends of link arms are raised into position over and toward the drive roller where the pressure rollers press the sheet against the drive roller. The suction cups separate from the sheet before the pressure rollers press the sheet against the drive roller. This may be accomplished by terminating suction applied to the suction cups.
It was discovered that the just described method of controlling the pivoting of the pivotably mounted suction cup support member, while satisfactory for most purposes, does not provide the most ideal adjustable control of the suction cup positions to ensure the most reliable removal of the bottommost sheet in a stack of sheets having all ranges of flexibility. For example, while the elevation of the abutment shoulders controlling the pivotal movement of the suction cup support member are adjustable as described, this adjustment only affects the degree of suction cup pivot action. There was no convenient progressive manual adjustment or control over the peak elevation of the link arms and the suction cups pivotally carried thereon. Such control was found to be useful in assuring separation of the bottommost sheet for a greater range of sheet flexibilities.
There was also no control over the angle of the suction cups when they were lowered from their peak positions to bring the front end of the sheet against the drive roller as described. When the sheet material is a fairly rigid material, as the sheet contacts the top surface of the drive roller it was found that the forces reacting on the sheet as it was pulled down upon the drive roller sometimes caused a premature separation of the suction cups from the rigid sheet before suction thereto was terminated and before the sheet could be contacted by the pressure rollers. The result was that the rigid sheet could spring upward out of the path of movement of the pressure roller where it would not be feedable by the drive roller and thus cause jamming of the machine.